PS1003 Andrew: Sensation and Sensory Processing II Flashcards
1
Q
What is the primary auditory pathway?
A
Cochlea- in the ear. Travels through the vestibulo-cochlear nerve (CN V III). Tthis projects to the cochlear nuclues, and then the superor olivary nucleus at the pons where there is cross over. (After this point it is binaural- so comes from both ears). It than travels to the inferior colliculus and then the medial geniculare nucleus as the thalamus finally to the auditory cortex.
2
Q
What is the Cochlea?
A
The sense organ in the ear
3
Q
What happens in the cochlea?
A
sound waves are converted into vibration in the basilar membrane.
4
Q
What is the organ of corti which is located in the the cochlea?
A
It is the sensitive element in the inner ear and can be thought of as the body’s microphone.
5
Q
What does the hair cells in the organ of Corti do?
A
It transduces movement of basilar membrane into electrical signal.
6
Q
What is the basilar membrane?
A
The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani
7
Q
Where is high frequency sound transduced?
A
At the base of the cochlea
8
Q
What is low frequency sound transduced?
A
At the apex of the cochlea
9
Q
Where is sound transmitted along?
A
the vestibule-cochlear nerve
10
Q
Where does auditory processing take place?
A
It was originally thought to be in auditory cortex, however found that the initial processing occurs in pons and thalamus.
11
Q
Where is the dorsal stream in auditory processing?
A
The parietal lobe
12
Q
What is the dorsal stream responsible for in auditory processing?
A
Spatial analysis- where the sound is coming from- able to locate the sound (where)
13
Q
What is the ventral stream in auditory processing?
A
Temporal lobe
14
Q
What is the ventral stream in auditory processing responsible for?
A
Component analysis- analysis of what the sound is (what)
15
Q
What is one cause of deafness: Conduction deafness
A
disorders of the outer or middle ear, which prevent sound vibrations reaching the cochlea
16
Q
What is one cause of deafness: Sensorineural deafness
A
an inability of the auditory nerve fibres to be excited in the normal manner
17
Q
What is one cause of deafness: Central deafness
A
damage to auditory brain centres and seldom a simple loss of hearing
18
Q
What is the localisation of sound dependent?
A
It is dependent on different characteristics of a sound arriving at each ear
19
Q
Localisation of sound: what is intensity difference?
A
difference in intensity of the sound between the two ears
20
Q
Localisation of sound: what is latency?
A
Phase shift between the two ears- due to the slight
21
Q
What is the duplex theory?
A
Sound location depends on a combination of intensity and latency
22
Q
What information does the vestibular organ recieve?
A
Sensory information about motion, equilibrium, and spatial orientation is provided by the vestibular apparatus, which in each ear includes the utricle, saccule, and three semicircular canals.
23
Q
What do the semi-circular in the vestibular organ do?
A
detect head rotation and tilt around three axes
24
Q
What is the pathway for detecting head movement?
A
Head movement- movement of endolymph- displacement of capula- stimulation of hair cells- activation of CN VIII- information transmitted to brain
25
What and where is endolymph?
Endolymph. Cross-section of cochlea. (Endolymph is located in the cochlear duct - the light green region at the middle of the diagram.) Endolymph is the fluid contained in the membranous labyrinth of the inner ear.
26
What is the cupula?
vestibular system: sense of spatial orientation
27
What is CN VIII?
The crainal nerve VIII, also known as the Vestibulocochlear nerve and brings sound and information about one's position and movement in space into the brain.
28
What are the vestibular pathways?
information comes in through the CN VIII (vestibulocochlear nerve) this is processed through the vestibuler nuclei in the brainstem (and motor thalamus) to the vestibulo ocular reflex, as well. CN VIII information also goes through the cerebellum to the cortex (which has info from the motor thalamus) to the balance reflex
29
What is the vestibulo-ocular reflex?
The vestibulo-ocular reflex. A rotation of the head is detected, which triggers an inhibitory signal to the extraocular muscles on one side and an excitatory signal to the muscles on the other side. The result is a compensatory movement of the eyes. Basically helps to track movement.
30
How are the vestibulo-ocular reflex and balance reflex different from normal reflexes?
They are not just through the spinal cord but though centres of control (e.g. cortex) however we still do not need to think about the action.
31
What is the balance reflex?
Postural reflexes are responsible for the subconscious maintenance of the body’s posture when movement and position is altered and they ensure that the body remains upright and aligned. It is the effects of gravity on the body which triggers their response and so these reflexes do not begin to develop until after the baby is born.
32
What is the balance reflex pathway?
vestibular organ feeds into the vestibular nuclei which is spilt into two areas, medial (closer to the midline) this controls neck muscles and therefore head orientation. The second area is lateral (further from the midline), therefore control peripheral muscles which is in charge of postural muscles and balance.
33
How is motion sickness caused?
May be caused by a mismatch between visual information and information from the vestibular organ- similar to that of an ear infection but in that case the information the vestibular organ is receiving is incorrect due to infection
34
What are the sensory receptors pathways?
The sensory receptors that are for peripheral goes through the spinal cord and that in the cranial (e.g. tongue) feeds into the brain stem. Project to the thalamus, to the somatosensory cortex which then goes to either the cingulate cortex of other `cortical areas.
35
Where is the somatosensory cortex located?
It is a band of tissue around the post central gyrus, which is behind the central sulci and at the front of the parietal lobe.
36
How are the motor and somatosensory homunculus similar?
The tongue and hands are very sensitive.
37
What are peripheral sensory receptors?
They are free nerve endings (pain and temperature). It is the skin which has specific receptors
38
What is the Merkel's disc?
Responsible for touch and deep pressure
39
what is the Meissner's corpuscle?
Responsible for touch and things on the skin- so very light and sensitive
40
What is the pacinian corpuscle?
Responsible for vibration- so movement along the skin
41
What is the Ruffini's ending responsible for?
Responsible for stretch, so the stretching of skin at the fingers for example when they move
42
What are hair follicle receptors responsible for?
The detection of movement of hair.
43
what is a Nociception?
the perception of a noxious stimulus- an objective measure
44
what is pain?
the subjective 'feeling' due to a noxious stimulus
45
What is analgesia?
the modulation of nociception or pain
46
Why is pain subjective?
Because people have different pain thresholds and this also differs within an individual over time.
47
Nociception: what is transduced?
Transduction of of a noxious stimulus into electrical activity in appropriate nerve endings e.g might be temperature so aware that something is hot
48
Nocicpetion: what is transmitted?
Transmission of the electrical signal through nerves, to the spinal cord and the brain (in somatosensory cortex)
49
Nocicpetion: what is the importance of the cingulate cortex?
Perception of the noxious stimulus in brain areas, and the conscious ‘feeling’ of pain- within the primary somatosensory cortex but the actual feeling is within the cingulate
50
Nocicpetion: what modulates?
Modulation of signal at various levels (analgesia)
51
What is noxious stimuli?
A noxious stimulus is "an actually or potentially tissue damaging event."
52
What activates peripheral nociceptors?
Noxious stimuli
53
Are peripheral nociceptors polymodal or unimodal?
Mostly polymodal but there are a few that are unimodal
54
What does it mean for nociceptors to be polymodal?
It responds to many different types of stimuli such as mechanical, thermal and chemical. They cannot discriminate at what is causing the pain but there there is a noxious stimulus
55
What does it mean for nocicpetors to be unimodal?
they will only signal one type of stimuli
56
What are pain responses mediated through?
through histamine, prostaglandins, bradykinin etc. and other peptides found within the skin
57
In terms of pain what responses do we have?
The immediate response of pain and the inflammatory.
58
What happens during an inflammatory response?
The different neurotransmitters and secondary messengers are responding to this inflammatory response and this response is protective, not just comfort but enable tissue to repair and this is mediated at the level of the skin.
59
Why can an anti-histamine drug reduce inflammatory pain?
As the response is mediated through histamine which causes the pain.
60
What is peripheral transmission?
peripheral nociceptive fibres enter spinal cord through the dorsal root and terminate in the dorsal horn/ Synapse in the dorsal horn with both ascending axons and spinal interneurons- these complete the reflex loop
61
What is an example of peripheral transmission (reflex loop)?
to remove finger from source of heat without information needing to go through the brain
62
what is the medulla?
the inner region of an organ or tissue, especially when it is distinct from the outer region or cortex
63
What happens during central transmission?
Ascending axons cross midline and ascend through the (anteroelateral column) spinal cord. Terminates in thalamus
64
What happens at the brainstem during central transmission?
Collateral terminations take place. Projects from brainstem to thalamus
65
What happens at the thalamus during central transmission?
Projects information to somatosensory cortex and cingulate- reciprocal connections (comes back to thalamus for modulation)
66
What is the ventricular system in the brain like?
There lateral ventricles on the side which runs through the third ventricle goes through the duct, the goes through the fourth ventricle then goes to the spine. Almost like a circulation system. If the cerebral acqueduct (between third and fourth ventricles) becomes block the circulation is lost.
67
What happens within the channel of the spinal cord if it is damaged?
It can affect motor abilities
68
What surrounds the cerebal acqueduct?
Periacqueductal grey matter
69
What is the ventricular system
The ventricular system is a set of four interconnected cavities (ventricles) in the brain, where the cerebrospinal fluid (CSF) is produced
70
Where is the perception of pain located?
Perhaps in the cingulate cortex
71
What is an example where the cingulate cortex may be activated?
In people who have illusory pains e.g. phantom limbs
72
What is the cingulate cortex involved in?
in creating the subjective experience
73
What is pain based on?
Pain is a subjective experience based on the information received from nociceptive fibres
74
How may the experience of something such as illusionary pains exist?
The brain can be fooled into thinking something is painful, even though no tissue damage has occurred
75
What is opium comprised of?
Comprises the dried sap of the opium poppy
76
How does opium act?
Sedative and analgesic
77
What are the two main active components of opium?
Morphine (~10%)- opium like drugs
| Codeine (~0.5%)
78
What does analgesic mean?
(of a drug) acting to relieve pain
79
What are two examples of opioid drugs?
Heroin and Methadone
80
How does morphine act?
It acts through binding sites in the brain and the spinal cord
81
Is morphine an agnoist or antagnoist?
morphine is an agonist
82
Why is morphine an agonist?
blocked by naxolone (antagonist)
83
Is morphine endogenous?
no (is not produced naturally in the body)
84
What are examples of isolated endogenous opioids?
Enkephalins, endorphins, dynorphins
85
What specific receptors have been found in opioids?
µ (mu) receptors, δ (delta) receptors, κ (kappa) receptors
86
What are µ (mu) receptors most sensitive to?
most sensitive to morphine and to endorphins.
87
What are δ (delta) receptors most sensitive too?
most sensitive to enkephalins
88
What are κ (kappa) receptors most sensitive too?
most sensitive to dynorphins
89
Where is morphine injected and why?
Morphine injected into lateral ventricles relieves severe pain
90
How do doses change for systemic injection (food/drugs etc) than peripheral injection (close to nerves)
Need less for peripherally as it is acting in the brain and so it is effect at doses 10 fold lower than peripheral and systemic.
91
What induces analgesia?
• Intracerebral injection of morphine induces analgesia
92
Which areas are analgesia induced?
periaqueductal grey matter (PAG)
periventricular grey matter (PVG)
rostroventral medulla (RVM)
93
Is analgesia an active process?
yes
94
What blocks the effects of morphine?
naloxone- use to define if soemthing is working through an opioid system.
95
What happens if Naloxone is injected into the PAG, PVG or RVM?
It partially reverses analgesic action of systemically administered morphine. As it is partial means that there is another point where opioid induced analgesia takes place.
96
Which areas of electrical stimulation applied to supress pain perception in the brain?
periaqueductal grey matter (PAG)
periventricular grey matter (PVG)
rostroventral medulla (RVM)
means that there is a pathway which dampens down nocicpetor pain, where morphine also works along.
97
What does electrical stimulation to localised brain areas do?
It mimics neuron activity
98
Similarities between opioid and stimulation produced analgesia?
Effective loci are the same (PAG, PVG and RVM).
99
Similarities between opioid and stimulation produced analgesia?
Both blocked by naloxone
100
Similarities between opioid and stimulation produced analgesia?
• Combining sub-analgesic levels of both produces analgesia- so reduce level of morphine and intensity of stimulation- in themselves neither would be efficient in producing analgesia which suggests needs both
101
Similarities between opioid and stimulation produced analgesia?
Cross-tolerance develops between the two- less and less effective. can immune to morphine need higher and higher dosages
102
Similarities between opioid and stimulation produced analgesia?
Both effects cause blockade of spinal reflexes, therefore we see that it is mediated at the level of the spinal cord
103
What is the dorsolateral funiculus?
anatomical nomenclature for a cordlike structure or part, especially one of the large bundle of nerve tracts that make up the white matter of the spinal cord. adj. adj funic´ular.
104
What is stimulus produced analgesia mediated through?
opioid mechanism so producing analgesia in the brain and is within the brain
105
What is stimulus produced analgesia mediated through?
opioid mechanism so producing analgesia in the brain and is within the brain
106
Levels of opiniod analgesia: what happens at the supraspinal?
opioid receptor activation in brain stem, then mediated via spinal cord mechanisms and the mu-receptor mediated (i.e. endorphins
107
Levels of opiniod analgesia: what happens at the spinal?
opioid receptors activation in spinal cord. Delta- & kappa- receptor mediated (enkephalins & dynorphins)
108
Levels of opiniod analgesia: what happens at the hormonal?
stress-induced analgesia is reversed by naloxone- see as the battlefield analgesia e.g. during battle cannot feel the pain- the stress induced analgesia is what dampens down the pain so do not feel the pain straight away. It is reversed by removal of adrenal glands- in the kidney- involved
109
Non-opioid analgesia: what happens at the brainstem?
Noradrenaline and 5HT (serotonin) modulate analgesia especially in PAG and PVG. However, Mechanism not clearly understood
110
Non-opioid analgesia: what happens at the spinal cord?
Noradrenaline (neurotransmitter) injected into spinal cord blocks responses to noxious stimuli. 5HT injected into spinal cord is analgesic which blocks spinal cord nociceptive neurones and blocks spino-thalamic neurons
111
Alternative methods of analgesia: what is Transcutaneous electrical nerve stimulation (TENS)?
Alters nociceptive signal to brain, or brain’s perception of pain. Mechanism unclear but may activate endogenous opiate systems
112
Alternative methods of analgesia: what is Acupuncture
Greater than 80% increase in pain threshold.
Increased enkephalin levels in the brain.
Increased biosynthesis of enkephalins.
Effects were enhanced by enkephalinase inhibitors.
May be mediated via enkephalin release in PAG and PVG.
113
Alternative methods of analgesia: what is Placebo
May activate endogenous pain-control systems- can be strong in some places
114
Alternative methods of analgesia: what is Hypnosis
alters brains perception of pain
115
Alternative methods of analgesia: what is Stress
both opiate and non-opiate mechanisms
116
Alternative methods of analgesia: what is Cognitive
may activate endogenous pain-control systems
117
Summary:
Summary
• Sensory perception occurs at peripheral modality-specific receptors
• Information transmitted to the brain through cranial or spinal nerves
• Makes connections in brainstem and thalamus
• Information enters cortex at unimodal primary sensory cortices
• Hierarchical processing occurs in unimodal association cortices
• Highly processed unimodal signals enter multimodal association cortex, where sensory integration occurs
118
What are the neurotransmitters at the spinal cord?
glutamate and substance p
